System and method for characterizing a seismic acoustic signal

Abstract

A method for correcting for distortions in a seismic acoustic wavefield produced by a seismic vibrator that is immersed in a fluid, the method comprising: applying a pilot signal to the vibrator such that an acoustic wavefield travels outwards from the interface between the vibrator outer surface and the fluid: using a sensor located within the fluid so as to be sensitive to a property of the wavefield in the fluid to monitor the property of the wavefield as a function of time: and using the measured property to determine a change in wet volume of a component of the vibrator as a function of time V(t) or derivatives of V(t), and using the determined wet volume V(t) or its derivatives to correct for distortions in the seismic data produced by the vibrator.

We claim: 
     
       1. A method for correcting for distortions in a seismic acoustic signal produced by a seismic vibrator immersed in a fluid, the method comprising:
 determining a relationship between a pilot signal as a function of time q(t) and a wet volume as a function of time V(t); and 
 based on the determined relationship, applying a non-linear transformation, T, to the pilot signal so that the wet volume V(t) becomes a linear function of the modified pilot signal. 
 
     
     
       2. The method according to  claim 1 , wherein determining the relationship between the pilot signal and the wet volume, and thus determining the non-linear transformation to apply, comprises performing a computer simulation of the behaviour of the vibrator. 
     
     
       3. The method according to  claim 1 , wherein the non-linear transformation is determined by experiment. 
     
     
       4. The method according to  claim 1 , wherein the non-linear transformation is determined by applying the pilot signal to the seismic vibrator such that an acoustic wavefield travels outwards from an interface between the seismic vibrator outer surface and the fluid,
 using a sensor to monitor a property of the acoustic wavefield within the fluid as a function of time, 
 using the measured property to determine the wet volume of the seismic vibrator as the function of time V(t), and 
 determining the non-linear transformation from V(t) and the pilot signal q(t). 
 
     
     
       5. The method of  claim 4 , wherein the sensor is located at a distance of greater than 5 meters from the seismic vibrator outer surface and the fluid is water. 
     
     
       6. A system configured to correct for distortions in a seismic acoustic signal produced by a seismic vibrator immersed in a fluid by being configured to:
 determine a relationship between a pilot signal as a function of time q(t) and a wet volume as a function of time V(t); and 
 based on the determined relationship, apply a non-linear transformation, T, to the pilot signal so that the wet volume V(t) becomes a linear function of the modified pilot signal.